The present invention relates to safety applications in industrial environments, and in particular, to distribution networks for safety sensors and devices.
Industrial environments typically include numerous mechanical operations, such as doors opening and closing, conveyor systems moving, and so forth. Such mechanical operations may be hazardous if the state is not known or fully appreciated. For example, if a door in the industrial environment is propped open, such as for inspection or diagnostics of machinery, and a conveyor system moves, or if a door in the industrial environment is closed, such as at a receiving station, and the conveyor system moves, a catastrophic condition could potentially result, such as human injury and/or property damage.
Safety sensors and safety distributions systems are known techniques for increasing the protection of personnel and equipment in such environments. Safety sensors may monitor, among other things, the status of doors and the motion of equipment. Safety sensors may comprise, for example, various modules with integrated proximity sensors, connectors or other mechanisms for detection, and switches for electrical signaling. Safety sensors are typically dispersed throughout the industrial environment and often attach to a one or more centralized safety distribution boxes as part of a safety sensor distribution network.
In operation, a safety signal may be routed to each particular safety sensor and back, such that if electrical continuity of the safety signal is detected, a safe condition is believed to be likely. On the other hand, if electrical continuity of the safety signal is not detected, such as the safety sensor breaking electrical continuity due to detection of an open door that should be closed, an unsafe condition may be presumed, an alert may be triggered, and the related industrial process may be stopped.
For additional safety, redundant signals may also be routed to each particular safety sensor and back, such that if electrical continuity is lost among any one of the safety signals, an unsafe condition may again be presumed. In addition, the safety signals are often routed serially through each safety sensor via the safety distribution box, such that if electrical continuity is lost due to any one of the safety sensors, an unsafe condition may again be presumed.
The safety distribution box often, in turn, couples to a power supply, a dedicated safety relay or safety programmable logic controller (“PLC”) and/or a general PLC. PLC's typically include a processor executing software stored in memory and numerous input and output connections for interacting with the industrial environment, including for monitoring safety signals and triggering an alert upon detecting an unsafe condition.
Shorting plugs that electrically short together safety signals are also typically used in such environments for maintaining flexibility. If, for example, a safety sensor is no longer needed, the safety sensor may be removed and a shorting plug may be installed in the old safety sensor's place at the safety distribution box. As such, electrical continuity of the safety signals may be maintained.
However, bypassing safety sensors that are still in use in the industrial environment with shorting plugs results in a loss of safety monitoring in the system. As a result, the potential for catastrophic conditions occurring increases.